This invention relates to an improved diaphragm valve.
It has been a problem in the art to provide diaphragm valves which are chemically inert, have very little "dead space" within, and are reliably operated for many thousands of cycles without maintenance requirements. Such valves are useful in a great many applications. However, the above-recited characteristics are particularly well suited to use in liquid chromatographic apparatus. Such apparatus handles extremely small liquid flow streams. Moreover, into such streams are injected samples for analysis which are frequently on the order of a microliter in volume.
Such samples must move smoothly through valving without undue mixing and without loss. Because of the variety of carrier liquids and sample chemicals used by a chromatographer, the valves must be constructed of chemically inert materials. Moreover, since the user is often a chemist or biologist in a laboratory with limited maintenance capabilitites, it is desirable that valves installed in the apparatus last for the lifetime of the apparatus in which they are installed.
The valves in the prior art which are useful at high pressures in such applications rely on metal diaphragms one of the best of which is described in U.S. Pat. No. 3,918,495 to Abrahams, Such reliance is necessary because such chemicallyinert materials as polytetrafluoroethylene (Teflon) excessively and, at fluid operating pressures which are from 3000 to 8000 psi, extrude right out of the valve structure. Moreover, the highly localized pressures which are inherent in simple, low-volume, flow-characteristics of such valves have required the strength of a metal diaphram. Nevertheless, chemically-inert metal diaphragms are subject to deterioration because of work hardening and, moreover, are less desirable than polymeric materials because of their inability to seal around any specks of dirt which may get between the sealing face of the diaphragm and the structure of the valve. At high pressures, this rigidity of useful, corrosion-resistant metals is such as to allow damage to, and/or leakage in, the valve.